Electrical heating apparatus



E John M. Ed

Y ffm ATTORNEY United States Patent ELECTRICAL HEATING APPARATUS John M.Edwards, Ruxton, Md., assignor to Westinghouse Electric Corporation,East Pittsburgh, Pa., a corporation of Pennsylvania Application April21, 1953, Serial No. 350,131

3 Claims. c1. 219-10.75)

My invention relates to electrical heating apparatus and relates, inparticular, to apparatus for heating by high frequency induction thevalve seats of internal combus tion engines and similar surfaces ofrestricted area.

The repeated impacts which the valves of internal combustion enginesimpose on their associated valve seats makes it necessary that thesurfaces of the latter be of hardened steel. It has been conventionalpractice in the automobile and other industries to make the valve seatsas separate parts which can be heat treated and hardened before assemblywith the engine body. It would, however, be possible to save materialand expense if the valve seats could be made integral with the engineand hardened in place. Attempts have been made to do this by inductionheating, using currents in the audio frequency range, i. e., not over15,000 cycles per second; but it has been found impossible in thesearrangements to avoid heating a large volume of the engine wall back ofand around the valve seat, with a consequent high expenditure of heatingenergy and general expensiveness in the process.

One object of my invention is accordingly to provide an arrangement forheating valve seats and similar restricted surfaces of metallic bodiesby induction heaters so designed as to confine the high temperature to avery restricted volume of metal in the immediate vicinity of the desiredsurface.

Another object is to provide an induction heating arrangement for metalsurfaces which shall confine high temperature to a region of very smalldepth behind the surface.

Another object is to provide an arrangement for hardening or otherwiseheat treating valve seats of internal combustion engines which shallconfine the region of high temperature to the metal in the immediatevicinity of the valve seat surface.

Another object is to provide a new and more economical arrangement forheat treating valve seats of internal combustion engines.

Still another object is to provide an improved arrangement for heattreating valve seats or similar restricted surfaces of internalcombustion engines.

Other objects of my invention will be apparent upon reading thefollowing description taken in connection with the drawings, in which:

Figure 1 is a schematic showing in perspective of an apparatus embodyingthe principles of my invention for heat treating the valve seats in aninternal combustion engine head;

Fig. 2 is an enlarged perspective view of the induction heating coilused in the Fig. 1 apparatus; and

Fig. 3 is an enlarged sectional view showing the heating coil inoperating position for heat-treating the valve seat in the Fig. 1apparatus.

In general, I attain the above-mentioned objects by employing radiofrequency currents, i. e., currents of frequency above about 50kilocycles, traversing inductors of conical or other form adapted toproduce localized magnetic fields concentrated on the surface to beheated, and maintain these currents for such a short time that the heatinflow is cut off before the high-temperature zone produced in thesurface layer has time to extend very far below the metal surface.

Referring to the drawings in detail, the engine block 1 to be heattreated is held by a table or other suitable support 2. The valve seats3 which are to be heat treated are of circular section having thegeneral contour indicated in Fig. 3 and their internal diameter is ofthe order of an inch at the narrowest section. To obtain close couplingbetween the heating coil 4 and the surface of valve seat 3, and toinsure uniform distribution of heat around the circumference of theseat, considerable precision in relative positioning of the coil andvalve seat is required. My experience indicates that this precision maybe attained most readily by making the support 2 movable while the coil4 is held stationary on a rigid support arm 5 which projects from thestationary transformer 6. Such a movable carriage or support 2 might,for example, comprise a base 7 on which the transformer 6 rests andhaving a frame 8 movable on one coordinate axis by threaded shafts like9, a plate 11 moved along a second coordinate by threaded shafts like12, and vertical screws 13 controlling the height above base 7 of enginesupport 2. Other arrangements for the desired adjustable positioning ofsupport 2 could readily be devised by men skilled in the art.

The transformer 6 has a suitably low-voltage secondary winding 15terminating in strap copper leads 16 which extend on opposite sides ofthe arm 5 which is of insulating material. The primary winding 17 oftransformer 6 is connected to a suitable generator 18 of radio frequencyoscillations which is controlled by a supply line switch 19 and a timer21 which is, in turn, controlled by a foot-switch 22. The timer 21 maybe set to cause generator 18 to impress radio frequency voltage ontransformer 6 for any desired interval, usually of the order of 20seconds.

On the ends of strap leads 16 are attached the vertical ends of theheating coil 4 which has the form shown in Figs. 2 and 3. This coil 4comprises short vertical leads and two complete turns, in planes normalthereto, of copper tubing which may be of one-eighth inch outsidediameter and about .020 wall-thickness for treating valve seats of thesize mentioned above. The planes of the two turns may be aboutthree-eighths of an inch apart and the vertical leads about ninethirty-seconds apart between the nearest portion of their surfaces. Theoutside diameter of the upper, and larger, turn may be about one andnine-sixteenths inches while the outside diameter of the lower turn maybe about one and one-eighth inches. As is evident from Fig. 2, onevertical lead turns radially and continues as the upper turn; is thenbeat sharply inward parallel to said radial portion until near thecenter of the coil where it turns downward to the level of the lowerturn. It then extends radially outward, turning sharply to form thatturn, then extends radially inward nearly to the center where it turnsupward to form the other vertical lead and attach to the end of strap16. At their nearest points, the radial portions of the coil may bespaced about one thirty-second of an inch apart.

The ends of the copper tubing above their junction with the straps 16are bent outward for connection to ducts 23 for cooling fluid, whichflows continuously through the copper tubing of coil 4.

To harden a valve seat of the size mentioned above, the support plate 2is adjusted so that it is positioned relative to heating coil 4 about asshown in Fig. 3, and foot switch 22 is then closed. Timer 21 then causestransformer 6 to produce a flow of about 450 amperes of five hundredkilocycle current in coil 4 for about 20 seconds. The eddy currentsinduced in the valve seat 3 generate a large amount of heat with extremerapidity in a very thin surface layer of the valve seat to which thesecurrents are confined by slrin-etfect. This thin layer is thus raised toa sufficient temperature to harden it, and this happens before the hightemperature in the thin layer has time to cause much heat flow intounderlying layers beneath the surface. The immediate interruption ofcurrent flow in heating coil 4 by action of timer cuts off furthergeneration of heat in the surface layer and the high temperature therequickly disappears, thus pre venting substantial rise in temperature ofany layers except the thin surface zone just mentioned. Thus almost allthe electrical energy supplied is employed in raising temperature of thethin surface layer and very little wasted in the undesired heating ofthe remainder of the engine wall. A great saving in electric power andgreat reduction in size of the electrical equipment, compared with audiofrequency heating, is thus attained.

Rise in temperature of underlying and interior layers of the metal isalso minimized by quench spraying the metal body the instant currentflow in heater 4 is cut off. For this purpose, a spray-head 25 ispositioned to project water or other cooling media onto the valve seatand adjacent portions of the engine head. Cooling fluid is suppliedthrough a duct 26 under control of an electrically operated valve 27.The latter is operated to project the quench stream by the timer 21 forany desired interval, preferably about 10 seconds, after it interruptscurrent flow in heater coil 4.

Although a specific embodiment of the present invention is shown anddescribed, it is to be understood that still further modificationsthereof may be made without departing from the spirit and scope of theinvention.

1 claim as my invention:

1. A heat treating apparatus for a valve seat having a surface to beheat treated, said apparatus comprising a radio frequency transformer, aheating coil having an axis and being connected to said transformer andsupplied thereby, said heating coil comprising two circular turns ofconducting tubing respectively positioned eoaxially in parallel planesand having in-leads extending along said axis, and adjustable supportmeans for supporting said valve seat with said surface being adjustablypositioned between the respective parallel planes of said turns of saidheating coil.

2. A heat treating apparatus for a valve seat having a circular surfaceto be heat treated, said surface hav- 5 ing an axis, said apparatuscomprising a radio frequency transformer, a heating coil connected tosaid transformer and supplied thereby, said heating coil having an axisand comprising two circular turns of conducting tubing respectivelypositioned coaxially and in parallel planes and having axially extendingin-leads, support means for supporting said valve seat with said surfacecoaxially positioned relative to said heating coil and between saidparallel planes, current supply means for supplying said transformerwith alternating current of a frequency in the order of five hundredkilocycles for a time period of the order of 20 seconds, and quenchmeans for cooling said valve seats after the termination of said timeperiod.

3. In heat treating apparatus for a valve seat having a circular surfaceto be heat treated, with said surface having an axis and internaldiameter, the combination of a heating member having an axis and a firstsection positioned in a first plane and a second section positioned in asecond plane, with said first plane being substantially parallel to saidsecond plane, adjustable support means for supporting said valve seatwith said surface coaxially positioned relative to the heating memberand between said first and second planes, said first section of theheating member having an external diameter which is smaller than saidinternal diameter.

References (Iited in the file of this patent UNITED STATES PATENTS2,378,890 Abe et al lune 26, 1945 2,397,629 Stevens Apr. 2, 1946 FOREIGNPATENTS 597,161 Great Britain Ian. 20, 1948 0 635,360 Great Britain Apr.5, 1950 OTHER REFERENCES High-Frequency Induction Heating, by Frank W.Curtis, second edition, 1950, page 151, McGraw-Hill Book 5 Company.

